ZRD - FAQ Tachometer Adjustment

Will my tachometer work correctly when I install a new alternator or regulator?

This question has multiple answers.

1. Current Yanmar engines have their tachometer driven directly from their engine's flywheel and do not use the white alternator stator wire to provide any input to the tachometer at all - so no adjustment should be required for if a Yanmar engine was installed correctly, but see 4 below if no initial adjustment was ever performed on your existing engine tachometer.

2. If the alternator you are replacing with a ZRD High Output Alternator or ZRD supplied Balmar Alternator, has the same number of poles (14), no changes or adjustment should be necessary, but see 4 below if no initial adjustment was ever performed on your existing engine tachometer.

3. If the alternator you are replacing has a different number of poles, you will need to adjust your tachometer using the procedure in 4 below.

4. If adjustment is necessary because your previous alternator has a different number poles, or your engine tachometer was never initially adjusted correctly, the following procedure explains how to synchronize your engine's rpm to the engine's tachometer.

TIF780 Infrared Phototachometer

First, so that we actually know that we are using correct data, you will need to have, borrow, or purchase a Photo Tachometer. I recommend you include one with your boat tools. They are not expensive and prove very valuable over time. Many tool suppliers including Sears (Craftsman) sell them. You cut off a small piece of reflecting tape that comes with the tool and stick it on the pulley (crankshaft, alternator, water pump, ...) you desire to check the RPM for. In this specific scenario, place it on your crankshaft pulley so that it is visible on a straight line from you. Point the photo tachometer at the flywheel (reflecting tape) and push the button. The phototachometer display will show your RPM digitally - exactly! Real simple.

Next, Once you know the accurate engine rpm, make very small 1/8" turns or so (There should be a "calibration/adjustment" screw on the back of your existing engine tachometer.) and watch what happens to the displayed rpm on your engine's tachometer. When your tach agrees with the optical tachometer, you are done.

If there is no adjusting screw on your existing engine tachometer, you will need to update your existing engine tachometer to a "programmable" one that allows adjustment.